[4.02] Pre-Impact Characterization of Comet Shoemaker-Levy 9

The pieces of Comet Shoemaker-Levy 9 (SL9) are due to collide with Jupiter over
five days in July 1994. Many models have been calculated
of what will be the effect on Jupiter's atmosphere from this
collision, but all such models assume the size and density of the
SL9 pieces for estimating the energy. However, such quantities
are unknown for SL9. HST has imaged the pieces but has
not resolved them. At McDonald Observatory, we have been attempting
to characterize the pieces by searching for molecular emissions
which are common for comets. We have used the 2.7\,m telescope
and Large Cassegrain Spectrograph (LCS), a long-slit CCD instrument.
Observations have been obtained in March 1993, February 1994 and March
1994 and more are planned for April and May 1994.
The spectra cover the wavelength range 3000--5700\AA\ at 7\AA\ resolution.
This region includes the important cometary emissions of OH, NH,
CN, C$_{3}$, C$_{2}$, and CO$^+$. No emissions have
been detected yet. From our observations
we have been obtaining upper limits for the amount of gas produced.
The current 2\,$\sigma$ upper limit for H$_{2}$O gas production
based on the upper limit for OH emission is
$5\times10^{26}$\,sec$^{-1}$.
In addition to the spectroscopic observations, we have been
obtaining images with a conventional plate camera on the
2.1\,m telescope and a Prime Focus CCD Camera on the 0.76\,m telescope
for astrometric purposes. With the CCD images we can determine the
colors of the individual pieces.